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+<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
+<html>
+<head>
+    <title>DDL for HDF5</title>
+</head>
+
+<body>
+<h1>DDL in BNF for HDF5</h1>
+
+
+<h2>1. Introduction</h2>
+
+This document contains the data description language (DDL) for an HDF5 file. 
+The description is in Backus-Naur Form.  
+
+<h2>2. Explanation of Symbols</h2>
+
+This section contains a brief explanation of the symbols used in the DDL.
+
+<PRE>
+    ::=                      defined as
+    &lt;tname&gt;                  a token with the name tname
+    &lt;a&gt; | &lt;b&gt;                one of &lt;a&gt; or &lt;b&gt;
+    &lt;a&gt;<FONT SIZE=1.7>opt</FONT>                    zero or one occurrence of &lt;a&gt;
+    &lt;a&gt;*                     zero or more occurrence of &lt;a&gt;
+    &lt;a&gt;+                     one or more occurrence of &lt;a&gt;
+    TBD                      To Be Decided
+</pre>
+
+<h2>3. The DDL</h2>
+
+<dir>
+<pre>
+&lt;file&gt; ::= HDF5 "&lt;file_name&gt;" { &lt;file_boot_block&gt;<FONT SIZE=1.7>opt</FONT> &lt;root_group&gt; }
+
+&lt;file_name&gt; ::= &lt;identifier&gt;
+
+&lt;file_boot_block&gt; ::= BOOT_BLOCK { &lt;boot_block_content&gt; }
+
+&lt;boot_block_content&gt; ::= TBD
+
+&lt;root_group&gt; ::= GROUP "/" { &lt;unamed_datatype&gt;* &lt;group_attribute&gt;* &lt;group_member&gt;* }  
+
+&lt;unamed_datatype&gt ::= DATATYPE "&lt;unamed_type_name&gt;" { &lt;compound_type_def&gt;+ }
+
+&lt;unamed_type_name&gt; ::= the assigned name for unamed type is in the form of 
+                      #oid1:oid2, where oid1 and oid2 are the object ids of the type
+
+&lt;compound_type_def&gt; ::=  &lt;named_scalar_type&gt; | &lt;named_array_type&gt;
+
+&lt;named_scalar_type&gt; ::= &lt;scalar_type&gt; &lt;field_name&gt; ;
+
+&lt;scalar_type&gt; ::= H5T_STD_I8BE | H5T_STD_I8LE | ...
+
+&lt;field_name&gt; ::= &lt;identifier&gt;
+
+&lt;named_array_type&gt; ::= &lt;scalar_type&gt; &lt;field_name&gt; &lt;dim_sizes&gt; ;
+
+&lt;dim_sizes&gt; ::= dimension sizes in the form of [dimsize1][dimzise2]..., 
+                where dimsize1, dimsize2 are integers
+
+&lt;group_attribute&gt; ::= &lt;attribute&gt; 
+
+&lt;attribute&gt; ::= ATTRIBUTE "&lt;attr_name&gt" { &lt;datatype&gt;    
+                                          &lt;dataspace&gt;   
+                                          &lt;data&gt;<FONT SIZE=1.7>opt</FONT>  } 
+// &lt;datatype&gt; and &lt;dataspace&gt; must appear before &lt;data&gt;.
+
+&lt;attr_name&gt; ::=  &lt;identifier&gt;
+
+&lt;datatype&gt; ::= DATATYPE { &lt;named_type&gt; } |        
+               DATATYPE { "&lt;scalar_type&gt;" }  |         
+               DATATYPE { &lt;compound_type_def&gt;+ }
+
+&lt;named_type&gt; ::= &lt;hardlink&gt;
+
+&lt;hardlink&gt; ::= HARDLINK { "&lt;abs_name&gt;" }  
+
+&lt;abs_name&gt; ::= object absolute name
+
+&lt;dataspace&gt; ::= DATASPACE { "&lt;dataspace_name&gt;" } |
+                DATASPACE { ARRAY &lt;current_dims&gt; &lt;max_dims&gt; } | 
+                DATASPACE { OTHER &lt;ds_definition&gt;+ } 
+
+&lt;dataspace_name&gt; ::= &lt;identifier&gt;
+
+&lt;current_dims&gt; ::= a list of integers in the form of (<i>i<FONT SIZE=1.0>1</i></FONT>, <i>i<FONT SIZE=1.0>2</i></FONT>, ... ),
+                   where <i>i<FONT SIZE=1.0>k</i></FONT> is an integer, <i>k</i> = 1,2,...
+
+&lt;max_dims&gt; ::= (<i>i<FONT SIZE=1.0>1</i></FONT>, <i>i<FONT SIZE=1.0>2</i></FONT>, ... ) where <i>i<FONT SIZE=1.0>k</i></FONT> is an integer or H5S_UNLIMITED
+
+&lt;ds_definition&gt; ::= TBD
+
+&lt;data&gt; ::= data {TBD}
+
+&lt;group_member&gt; ::= &lt;named_datatype&gt; | &lt;named_dataspace&gt; | &lt;group&gt; | &lt;dataset&gt; | 
+                   &lt;softlink&gt;
+
+&lt;named_datatype&gt; ::= DATATYPE "&lt;type_name&gt;" { &lt;compound_type_def&gt;+ }
+
+&lt;type_name&gt; ::= "&lt;identifier&gt;"
+
+&lt;named_dataspace&gt; ::= DATASPACE "&lt;dataspace_name&gt;" { ARRAY &lt;current_dims&gt; &lt;max_dims&gt; } |
+                      DATASPACE "&lt;dataspace_name&gt;" { OTHER &lt;ds_definition&gt;+ }
+
+&lt;group&gt; ::= GROUP "&lt;group_name&gt;" { &lt;hardlink&gt; } |
+            GROUP "&lt;group_name&gt;" { &lt;group_attribute&gt;* &lt;group_member&gt;* } 
+            
+&lt;group_name&gt; ::= &lt;identifier&gt;
+
+&lt;dataset&gt; ::= DATASET "&lt;dataset_name&gt;" { &lt;hardlink&gt; } |
+              DATASET "&lt;dataset_name&gt;" { &lt;datatype&gt;  
+                                         &lt;dataspace&gt; 
+                                         &lt;storagelayout&gt;<FONT SIZE=1.7>opt</FONT>
+                                         &lt;compression&gt;<FONT SIZE=1.7>opt</FONT>
+                                         &lt;dataset_attribute&gt;*
+                                         &lt;data&gt;<FONT SIZE=1.7>opt</FONT>  } 
+// Tokens within {} can be in any order  as long as &lt;data&gt; and &lt;dataset_attribute&gt;
+// are after &lt;datatype&gt; and &lt;dataspace&gt;.
+
+&lt;dataset_name&gt; ::= &lt;identifier&gt;
+
+&lt;storagelayout&gt; :: = STORAGELAYOUT &lt;contiguous_layout&gt;  |  
+                     STORAGELAYOUT &lt;chunked_layout&gt;  | 
+                     STORAGELAYOUT &lt;compact_layout&gt;  | 
+                     STORAGELAYOUT &lt;external_layout&gt; 
+
+&lt;contiguous_layout&gt; ::= {CONTIGUOUS}    // default
+
+&lt;chunked_layout&gt; ::=  {CHUNKED &lt;dims&gt; }
+
+&lt;dims&gt; ::= (<i>i<FONT SIZE=1.0>1</i></FONT>, <i>i<FONT SIZE=1.0>2</i></FONT>, ... ), <i>i<FONT SIZE=1.0>k</i></FONT> is an integer, <i>k</i> = 1,2,... 
+
+&lt;compact_layout&gt; ::= TBD           
+
+&lt;external_layout&gt; ::= {EXTERNAL &lt;external_file&gt;+ }
+
+&lt;external_file&gt; ::= (&lt;file_name&gt; &lt;offset&gt; &lt;size&gt;) 
+
+&lt;offset&gt; ::= an integer
+
+&lt;size&gt; ::= an integer
+
+&lt;compression&gt; :: = COMPRESSION { TBD }  
+
+&lt;dataset_attribute&gt; ::= &lt;attribute&gt; 
+
+&lt;softlink&gt; ::= SOFTLINK "&lt;softlink_name&gt;" { LINKTARGET "&lt;target&gt;" }
+
+&lt;softlink_name&gt; ::= &lt;identifier&gt;
+
+&lt;target&gt; ::= &lt;identifier&gt;
+
+&lt;identifier&gt; ::= string   
+// character '/' should be used with care. 
+
+</PRE>
+</dir>
+
+
+<h2>4. An Example of an HDF5 File in DDL</h2>
+
+<dir>
+<PRE>
+HDF5 "example.h5" {
+GROUP "/" {
+   DATASET "dset1" {
+      DATATYPE {
+         H5T_STD_I32BE int_name;
+         H5T_IEEE_F32BE float_name;
+         H5T_IEEE_F64BE double_name;
+      }
+      DATASPACE { ARRAY ( 5 ) ( 5 ) }
+      DATA {{0,0,1}, {1,1,0.5}, {2,4,0.333333}, {3,9,0.25}, {4,16,0.2}}
+   }
+   GROUP "group1" {
+      DATASET "dset2" {
+         DATATYPE {
+            HARDLINK { "/type1" }
+         }
+         DATASPACE { ARRAY ( 5 ) ( 5 ) }
+         DATA {{0,0}, {1,1.1}, {2,2.2}, {3,3.3}, {4,4.4}}
+      }
+   }
+   GROUP "group2" {
+      HARDLINK { "/group1" }
+   }
+   SOFTLINK "slink1" {
+      LINKTARGET "somevalue"
+   }
+   DATATYPE "type1" {
+      H5T_STD_I32BE int_name;
+      H5T_IEEE_F32BE float_name;
+   }
+}
+}
+</pre>
+</dir>
+
+<hr>
+<address>
+<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a>
+</address>
+
+Last modified:  28 October 1998
+
+</body>
+</html>